Process for dehydrogenation of hydrocarbons



' Jan. 16, 1945. w A SCHULZE ErAL 2,367,622

PROCESS FOR DEHYDROGENTION 0F HYDROCARBONS ',Fled Sept. 27, 1941 2Sheets-Sheet 1 JOHN C. HILLYER BY HARRY E DRENNAN ATI'ORN Jan. 16, 1945.w, A SCHULZE ErAL 2,367,622

PRocEss FOR DEHYDROGENATION oF HYDRocARBoNs Filed Sept. 27, 1941 2Sheets-Sheet 2 Patented Jan. 16, 1945 PROCESS FOR DEHYDROGENATION OF HYDROCARBON S Walter A. Schulze, John C. Hillyer, and Harry E.

Drennan,

Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of DelawareApplication September 27, 1941, Serial No. 412,636

3 Claims.

This invention relates to the catalytic dehydrogenation of hydrocarbonsto produce oleiins and diolens. It relates more specically to animproved process for the dehydrogenation of paraffin and/or olenhydrocarbons to produce diolens and has particular application to theproduction of diolens from low boiling aliphatic hydrocarbons of saidclasses.

In the preparation of valuable diolens by catalytic dehydrogenation, thecorresponding olens may be treated to yield dioleiins directly, or thecorresponding parains may be the starting material for a two-stagedehydrogenation treatment in which olefins are an intermediate productof the initial dehydrogenation. In the latter instance the olens may ormay not be segregated prior to conversion todiolens. The combination ofthe dehydrogenation treatment hydrogenation of paraiiins such as normalbuinto a'single operating stage wherein the paran-olen andolefin-diclefin conversions are concurrent, has'been described. However,such combinations of the concurrent reactions have usually encounteredserious difculties due to the fact that optimum conversion conditionsare quite different for the two dehydrogenation reacti'ons.` Thus theconditions of temperature, iiow rate, catalyst activity vand the likewhich promote satisfactory conversions of olens have previously causedoverconversion o'f parafllns with consequent losses due to cracking,carbon formation and the ensuing complications due to side reactions andcurtailed catalystlife.

An alternative procedure starting with lowboiling paratlins such asnormal butane has in-l volved the separation of the two dehydrogenationreactions into two operating stages wherebythe olens formed underoptimum conditions for paraiin dehydrogenation are segregated and usedas the feed stock for a second conversion step to produce the diolen.This procedure has been based on the necessity of having lowconcentrations of parans present during olefin de-v hydrogenation.Conversely, low concentrations of olens are desirable in the parailindehydrogenation step. This procedure introduces a dificult andrelatively expensive operation to segregate the. paraiiln and olefinstocks, but is often justified on the basis of improved yields andoperation. t

Because of the relatively higher conversion temperatures, the largeconcentrations of unsaturated hydrocarbons. and the instability of thereaction products, the dehydrogenation of. olefins is carried out at lowpartial pressures of reactants. In this manner excessive decompositanemay be conducted in the absence of a diluent with principal attentionbeing devoted to an eicient separation of olen products from the parainsfeed stock.

The application of catalytic dehydrogenation to the low-boilingparafiins and to the corresponding oleiins has developed certain novelop-` erating methods and processes which have been disclosed inco-pending applications Serial Numbers 352,786, 352,787, 353,961,353,962, and 355,- 710.' Said disclosures have dealt with the preferredcatalysts, methods of obtaining feed y stocks, and the operatingconditions for the dehydrogenation of low-boiling parains and olefinsrespectively. In general, the use of extremely acting catalysts atrelatively low temperatures for normal butane dehydrogenationhas beendisclosed. Further, the use of higher temperatures and catalysts oflower but maintained and f specic activity have been designated for thedeof normal butane step or secured from other.

sources is used as the diluent in the dehydrogenation of butenes. Thisprocess provides certain advantages in the physical and chemicalcharacteristics o1' the C3 hydrocarbon diluent, but the handling andrecycling of large amounts of Cs hydrocarbons represents a larger itemin plant investment and operating costs. It is an object of thisinvention 'to describe an improved method for the production of dlolensfrom corresponding parailins. vMore particularly.- it is an object ofthis invention to produce lower boiling aliphatic dioleiins such asbutadiene from corresponding paramns, such as butane.

One of the specific objects of this invention is to provide an efficientprocess for producing diolens such as butadiene by a two-stagevdehydrogenation of parains such as butane in which different catalyticand other conditions are utilized in each stage, said catalysts and thecondtions of their use being adapted to produce optimum results in eachstage and in the combination of steps hereinafter more fully described.

We have noted that from the standpoint of chemical and physicalcharacteristics, the `most promising diluent for olefin dehydrogenationis water vapor. This diluent may be cheaply provided in any desiredamounts and may be removed from the hydrocarbon stream by simplecondensation, thereby eliminating a large part of the compression andfractionation equipment necessary when other diluents are used. However,the use of water vapor has previously been condemned in the art becauseof its deleterious effects on the activity of conventionaldehydrogenation catalysts and hence on the conversions obtained by theuse of said catalysts in prior dehydrogenation processes.

By extensive investigation we have determined the extent to whichsubstantially all suggested dehydrogenation catalysts are susceptible todeterioration and loss of activity by water vapor, and the conditionswhich govern the use of water vapor in hydrocarbon conversions. We havediscovered certain new catalysts, furthermore, which -arewater-resistant and which may be satisfactorily employed indehydrogenation reactions in a manner hereinafter described. 'Iheapplication of our discoveries to the dehydrogenation of both paramnsand olefins and the improved dehydrogenation process thereby evolved aredescribed below in detail.

The conversion of paraffin hydrocarbons such as n-butane to oletlns ispromoted by dehydrogenation catalysts operating with maximum activity attemperatures below those causing excessive thermal or catalytic ruptureof the carbon chain. Said catalysts often exhibit suitable activity inthe temperature range of 850 to 1150 F. and produce substantiallyequilibrium conversion with moderate contact times. Said catalysts,however, are characterized by inhibition of activityv in the presence ofwater vapor so that even relatively minor amounts of steam inhibitconversion. We prefer, therefore, to perform the paraffin-olefinconversion in the presence of a, highly active although watersensitivedehydrogenation catalyst and 1' in the substantial absence of watervapor.

In the dehydrogenation of olefins to diolefins, however, we have foundthat at the temperatures of about 1100 to 1300 F. desirable forconversion, the presence of water vapor does not inhibit conversion whenthe catalyst is water-resistant either inherently or by reason of amodifying an effective method for the vconversion of butane to butadieneis described, in which the first stage of dehydrogenation produces afeed particularly suitable for the second stage of dehydrogenation andin which conditions in each stage are effective for maximum operatingefficiency, the combination of steps thus giving optimum results. By theuse of our invention, the necessity or desirability of segregatingolefins from paraflins prior to dehydrogenation is wholly or partiallyeliminated with consequent savings and simplification in operations:Also, the use of the steam diluent in olefin dehydrogenation tends toreduce the rate and amount of deposition of carbonaceous material on thecatalyst. This effect results in increased operatingcycles for thecatalyst as well as a reduction in the time required for reactivation.These and other advantages of our process will be apparent from thefollowing disclosure.

In a more specific embodiment, our process may include the followingsteps: 1) ldehydrogenation of n-butane over a water-sensitive catalystin the substantial absence of water vapor to producesubstantiallyequilibrium conversion to n-butenes; (2) treatment of the products from(1) to remove lower-boiling material from the C4 fraction comprisingsubstantially butenes and unconverted butane; (3) charging the C4fraction from (2) diluted with steam to a second dehydrogenation stageusing a -waterresistant catalyst to produce butadiene; (4) treatment ofproducts from (3) to segregate a C4 fraction comprising butadiene,butenes and nbutane; (5) removing the butadiene from-the pre-treatment.Said water-resistant properties are obtained by experimental selectionor by pre-treatment of certain catalytic materials to impartwater-resistance. In fact, we have discovered that the quality ofwater-resistance may be imparted in certain instances by treatmentsdesigned to produce stability at high temperatures and specific activityin certain valuable catalytic materials. We have further discovered thatin the presence of water vapor and a waterresistant catalyst, thedehydrogenation reaction is specific for olefins to the extent that thecorresponding parafllns if present in normal concentrations aresubstantially unconverted. This discovery makes possible thedehydrogenation of butenes, for example, in the presence of relativelylarge amounts of n-butane with excellent yields of butadiene andnegligible conversion of the parailln hydrocarbon. In such an operationC4 fraction of step (4) and returning the butenes and n-butane to thefirst and/or the second dehydrogenation stage for further conversion.

The process may be illustrated by reference to Figure 1 which is a flowdiagram of one arrangement of conventional equipment for application ofour invention to normal butane.

Figure 2 is a fiow diagram of an alternative manner of performing thesecond' stage dehydrogenation.

In Figure 1 the fresh n-butane feed enters by line I and passes toheater 2 where the charge is heated to reaction temperature. The hotvapors then pass by line 3 to catalyst cases l containing awater-sensitive dehydrogenation catalyst, and the-treated vapors exitthrough line 5 to cooler 6. A portion of the eluent vapors may berecycled through line 5A to the inlet of the catalyst cases. The cooledvapors from 6 pass through polymer separator 1 in which minor .amountsof heavy material are removed, then are compressed in unit 8, and passto accumulator4 9. The compressed gas then passes byline I0 to strippercolumn Il where C: and lighter material is removed by line I 2. Aportion of this latter stream which contains hydrogen may be returned tothe feed line l through line l! if dedred. The accumulator liquid yfrom9 passes to column li through line id, while the liquid from column iiis taken through -line I to column iti, a portion being returned throughline il to column ll as absorbent. Column I6 operates to yremove C3 andlighter hydrocarbons from the C4 mixture and the former material isremoved through line i8. The C4 mixture which is the bottoms fractionfrom column i8 is taken through line i9 to line Z as fresh feed to thesecond-dehydrogenation stage.

The second stage feed enters the heater 22 through lines and 2i togetherwith steam from line 23 and recycled material from line 55. Thebutene-butane-steam mixture is heated to reaction temperature and passesthrough line 2li to catalyst cases 25 filled with a water-resistantcatalyst. The treated effluents exit by line 26. and a portion thereofmay be returned to the catalyst case inlet through line 2'1.

Thevhot vapors passing through line 26 are chilled by Water injectionthrough line 28, and pass to condenser 29 wherein water vapor iscondensed and condensate removed through line 30. The hydrocarbon vaporsthen pass to compressor @i and accumulator 32. The material fromaccumulator 32 enters column 33 through lines 3d and 35, and said columnoperates to remove C2 hydrocarbons and lighter material overhead throughline 3S. taken through line 3'! to column 38 or zpartly as absorbentthrough line 39 to column 33. Column 38 operates to remove C3 andlighter material overhead through line dil, while the depropanizedliquid is taken through line il to solvent extrac- I tion unit t2.

in unit l2 a separation is made by a selective solvent between then-butane and the unsaturated C4 hydrocarbons. The n-butane which is notdissolved passes through line d3 and may be returned through line lili,and if necessary through dehydrator liti, to the rst dehydrogenationstage. The solvent passes from unit i2 through line it to stripper ilwhere the C4 unsaturates are separated, and the solvent is returned tounit t2 through line d8. The butenes-butadiene mixture thussubstantially freed of n-butane then is taken through line t@ andfractionated in column El! to separate butene-i as an overhead product.The'bottoms fraction comprising'butenes-Z and butadiene iswithdrawn'through line 5i to fractionator t2, where substantially purebutadiene is taken overhead through line 53 to storage and butenes-2pass through line 5d to recycle line 55 or through line 56 to chemicalextraction unit 5l. The butene-i stream passing from column Eid throughlines 5d and 59 is treated in chemical extraction unit 5l' for theseparation of the relatively low percentages of butadiene present in thebutene-l. The butadiene recovered therein from either or both of thebutene streams is removed through line d@ and the butenes pass throughline di to recycle line 55. The recycle material from line 55 isreturned to the second dehydrogenation stage for further conversion tobutadiene.

Various modifications of the process outlined in Figure l will beobvious from our disclosure and no attempt will bel made to discuss allthe possibilities within the scope of our invention.

For example, the separation of C3 and lighter material from the productsof dehydrogenation The liquid from column 33 is ond stage total C4mixture may be utilized without departing from the present disclosure.

Certain devices for obtaining essentially adi- 4 abatic reactionconditions in the second stage catalyst cases may be employedparticularly Well with steam diluent, such as the multi-point injectionof steam into different sections of the catalyst cases. In thisarrangement the steam may be superheated to or above reactiontemperatures in a separate furnace coil and injected into the catalystbed to offset falling temperatures due to endothermal heat of reaction.

This last-named arrangement is illustrated by the ow diagram of Figure2. This shows the parain-olencharge passing through line lili andadmixed with steam from line |02 prior to entering heating coil [03. Themixture is heated to reaction temperature, and passes through line liito catalyst cases m5. The concentration of the pre-mixed steam from line02 is adjusted somewhat below the desired eventual steam concentration.Additional steam from line |06 passes through auxiliary heating coil I01 and then after being heated up to or somewhat above the reactiontemperature attained by the vapors in lineil is injected into thetransfer line 104 and/or the catalyst cases as indicated through linesHi8 and ISA at a plurality of points, The eiiluent vapors may be dividedat the exit of the catalyst cases Ed with a portion being recycled toline mit throughy line Htl. The remainder passes through line Hi@ intowhich cooling water may be injected from line Hl, and thence throughline H2, condenser HS and line il@ to further processing for therecovery of butadiene as illustrated in Figure 1. The condensed water iswithdrawn through line H5.

n the rst stage of our process, the dehydrogenation to produce olens isdesirably performed in both stages may be performedin a singlefractionation or with other auxiliary operations such as refrigerationand the like. Similarly other methods for separating butadiene from thesecon substantially dry feed stocks at pressures of about atmospheric topounds gage. Temperatures and pressures are selected within a rangesuitable for the catalyst used, and temperatures within the range of 850to 1150 F. are ordinarily employed. At these conditions ow rates of theorder of l to 1) liquid volumes of hydrocarbons per hour per volume ofcatalyst are usually maintained. Particular conditions of flow rate,ternperature and pressure are usually chosen to conform to thecharacteristics of the specic catalyst used.

The water-sensitive catalysts which are useful in the first stage of ourprocess are those having suitable activity at temperatures below thosecausing excessive cracking of the paran hydrocarbone and capable ofpromoting substantially equilibrium conversion under the designatedconditions. Said catalysts include the conventional high-activitydehydrogenation catalysts such as metals. metal oxides or compositesthereof alone or supported on suitable carriers. Of particular value arethe oxides of aluminum and magnesium which possess considerable activityin themselves, and are preferably promoted with more or less minorquantities of oxides of metals of Groups IV, V, and VI of the PeriodicTable. Specic examples are alumina catalysts promoted with the oxides ofchromium and zirconium. Also of particular value are certain activechromium oxide catalysts with or withouty carriers. of valuablewater-sensitive catalysts are the natural mineral ores such as bauxiteand activated clays promoted with chromium or other metal oxides orsalts. g

These catalysts are characterized by loss of ac- Another class A.

y tivlty due to the presence in the hydrocarbon vapors of water vapor,even in relatively minor quantities at temperatures corresponding to therange of optimum activtiy. However, for the paraffin-olefindehydrogenation, said catalysts are preferred because of theirhigh-activity and satisfactory yields of olens without excessive loss ofcharge stock or oleflnic products through carbon and fixed gas formationand/ or polymerization reactions.

The effluent vapors from the first stage of our process are processed toseparate any high-boiling material formed by the catalytic treatment,and to remove propane and lower-boiling gaseous products. 'I'heseparation of light gases is indicated in two stages, and the gas fromthe deethanizing column containing hydrogen may be partly returned tothe feed stock vapors ahead of the catalyst to reduce the rate ofcatalyst poisoning. Precautions are observed in such an operation toavoid building up concentrations of hydrogen which will suppress thedehydrogenation reaction.

The completeness with which C3 hydrocarbons' are'separated from the.first stage eluents may vary somewhat, and the retention of apropylenepropane mixture inthe charge to the second stage may not beundesirable since said gases are essentially diluents in the secondstage dehydrogenation. Further, the propylene is a potential .hydrogenacceptor capable of promoting dehydrogenation. In fact, thedepropanizing step may be omitted following our first stage if desired,and the separation of C3 hydrocarbons performed following the secondstage. Our purpose is to remove the C3 hydrocarbons at at least onepoint in the system to prevent the pyramiding and recirculation of thisrelatively inert material which increases the compression requirementsof the process. Also, the substantially complete separation of propaneis desirable ahead of the dioleln purification steps indicated in oursecond stage.

In the operation of the second dehydrogenation step, the charge stock isprepared in such proportionsrthat the partial pressure of olefins-isless than one atmosphere and ordinarily in .the range of 0.2 to 0.5atmosphere. The other constituents of the mixture are principallyundonverted parafns and steam together with any C3 hydrocarbonsremaining in the product from the first stage. After steady stateconditions are obtained in an integrated operation, the relative propor-In the treatment of butane-butene-butadiene mixtures these operationsproduce a substantially propane-free mixture which may then be treatedby solyent extraction, azeotropic distillation or the like to producethe desired degree of separation and recovery of the parainichydrocarbons. In many cases it is desirable to segregate abutadiene-containing fraction substantially free of butane and foreconomic reasons. the butane `concentrate returned to the, first stageis ordinarily substantially denuded of butadiene. The recycled butaneconcentrate may contain varying amounts of butenes and, although weusually prefer to maintain a relatively low degree of unsaturation inthe feed to the first stage, the dehydrogenation will proceed as longvas equilibrium concentrations are not exceeded.

The recovery of diolefln from the resulting unsaturated hydrocarbonmixture may be effected by the methods illustrated or by other knownprocesses which produce substantially equivalent results. Thus, thefirst operation on a butenes-butadiene mixture may be a fractionation toseparate a bottoms fraction comprising butenes-2 and butadiene and anoverhead fraction comprising principally butene-l with minor amounts ofbutadiene. This overhead fraction may then be treated by a chemicalextraction process for the removal of butadiene, and the butene-lreturned to the second stage of dehydrogenation.

The bottoms product is then fractionated to produce Substantially purebutadiene as the overf head product, while the butenes-2 bottoms frac-'tion is returned to the second stage catalyst along with theabove-mentioned butene-l. Or, if desired, the butene streams may becombined ahead of the chemical extraction step to effect more completerecovery of butadiene.

In certain instances it may be desirable to treat the entire C4 mixturefrom the second dehydrogenation stage, without preliminaryfractionation, in a chemical extraction unit for the recovery ofbutadiene. In this embodiment the residue from the chemical separationunit comprises butenes and n-butane which may be recycled to either orboth of the catalytic treatments for further conversion, withprecautions being observed to avoid pyramiding of n-butane in the secondstage.

tions of parains and steam will only slightly vary according to thecomposition of the product. Thus with a vapor mixture charge to saidsecond stage containing 20 to 30 or more volume per cent of olens, theparainic hydrocarbon content may vary between 20 and 30 volume per centwhile the steam component amounts to 40 to 60 volume per cent. Theseexemplary volume ratios, however, may be varied with specific operationson .diierent low-boilingl parafn feed stocks and within the terms of ourdisclosure.

'The` vapor eflluents from the second catalytic treatment are cooled to4condense and separate Water andany high-boiling polymer or tar. Themethod of cooling may be designed to provide an )extremely rapidreduction of temperature such as the introduction of a quenching medium.After separation of the condensate, the hydrocarbon vapors arecompressed and processed to remove C3 and lower-boiling hydrocarbons andother gases in one or a series of stripping and/or fraictionationoperations.

The second stage of dehydrogenation is operated at low pressures ofabout atmospheric to pounds gage. Low total pressures' are desirable .toincrease the yield of diolefin. Also, since 4the partial pressure ofolens in the charge is ordinarily below 0.5 atmosphere, it is desirableto operate at low total pressures in order to have maximum volumeconcentrations of this component.

Higher temperatures are usually employed in the second Stagedehydrogenation than in the rst stage. I'hus, in order to obtainsatisfactory conversion of butenes to butadiene, temperatures of about1100 to 1300 F. are ordinarily employed. Flow rates used are between 1and l0 liquid volumes of hydrocarbon charge per hour per volume ofcatalyst. In terms of the total vapor mixture charged to the catalyst,space velocities of 500 to5000 are satisfactory under proper conditions.The particular combination of flow rate and temperature for a specificoperation will depend on the catalyst employed, the composition of thecharge, and on the degree of conversion desired.

The catalysts used in the second stage are those of satisfactoryactivity in promoting selective olen dehydrogenation at temperatures inthe range of 11.00 to i300" F. and in the presence of water vapor. Gfthe greatest value are catalysts prepared by the treatment of bauxitewith the hydroxides or oxides of barium and/ or strontium in such amanner that the adsorbent; mineral ore is impregnated with the metalcompound. Such a catalyst and methods for manufacturing it have beendisclosed in our co-pending application Serial No. 353,961 filed August23, 1940. In the prior disclosure the application of the catalysts tobutene dehydrogenation is described, but the present invention embodiesa valuable additional development in the use of same in general olendehydrogenation, particularly in View of the property ofwater-resistance disclosed herein.

The oxides of aluminum and magnesium have been found to give especiallysatisfactory catalysts, as have also those of zirconium and titanium.Both synthetic preparations of the substantially pure oxides, hydratedoxides, or hydroxides, and also natural mineral ores comprising theseoxides, can yield satisfactory catalys'ts. High porosity, or specificsurfaceand other qualifications of good catalysts are desirable in thesematerials, both before and after treatment to impart water-resistantqualities.

W e have found that various alkaline materials added to the untreatedcatalysts in such a manner as to impregnato the catalyst thoroughly,`

serve to impart the qualities of water resistance and selective olefindehydrogenation to a Varying degree. While catalysts can be prepared byimpregnating with alkali oxides,we have found the specic alkaline earthoxides and/or hydroxides of barium and strontium to be mostsatisfactory.

Catalysts prepared by impregnating bauxite with barium or strontiumhydroxides and/or oxides are water-resistant and do not lose activity incontact with steam at elevated temperatures. Further, these catalystspromote selective dehydrogenation in the presence of steam to such anextent that the butane in a butano-butene mixed charge is relativelyunconverted while excellent conversion of butenes to butadiene isobtained. Said catalysts are alsodeactivated with respect to craclringand/or polymerization reactions involving the hydrocarbon reactants orproducts.

In the catalytic dehydrogenation of butenes over the above-mentionedcatalysts certain benets have been noted from the use of water vapor asdiluent. Thus, while the dehydrogenation of butenes proceeds with goodconversion to butadiene, butane present in the mixture is relativelyunconverted although operating temperatures are usually over 180 F.higher than those used for butane conversion in our rst stage.- Also, aprolonged period of maximum catalyst activity for butene dehydrogenationis obtained when the preferred conditions are maintained. These benetsapparently are due to the use of steam in conjunction withwater-resistant qualities of our preferred catalysts and to tne lunctionof the water vapor in reducing tar and/or coke deposition on the`catalysts during the hydrocarbon conversion. This latter effect isresponsible both for prolonged operating cycles and greatly reduced timerequirements for reactivation.

The following examples will further illustrate specic applications ofour process, vwithout implying any particular limitations thereto.

Example I Normal butane was dehydrogenated over a bauxite-chromium oxidecatalyst containing 10 weight per cent of chromium oxide. Theclehydrogenation was carried out at a temperature of 110D F. and 25pounds gage pressure. At a ow rate of one liquid volume of charge perhour per Volume of catalyst, conversion amounted to 35 per cent per passof the n-butane with an emciency of about 80 percent based on thebutenes produced. The eilluent vapors from this rst dehydrogenationstage were cooled, compressed and fractionated to produce a C4 fractioncontaining about 30 mol per cent of butenes and about 70 mol per cent ofn-butane with minor amounts of C3 hydrocarbons and butadiene.

This mixture which constituted make-up feed to a seconddehydrogenationstage was combined with a recycle stream predominantly comprisingbutenes from said second stage and diluted with steam to reduce thetotal butenes content to 30 volume per cent. The charge compositionunder recycle conditions was approximately as follows:

Volume per cent Butenes 30 n-Butane 2l Steam 49 I This charge was heatedto 1185 F. and passed over a water-resistant catalyst consisting ofbauxite impregnated with 4.5 weight per cent of barium hydroxide at aspace velocity of 1150 and a pressure of 5 pounds gage. The eilluentswere cooled by direct water injection and the steam Volume per centButadiene 9-19 Butenes -46 n-Butane d5 The product representedapproximately 3() per cent per pass conversion of the butenes chargedand about 50 per cent efciency in the couver sion to butadiene.

The Ci fraction was then submitted to selective solvent extraction forthe separation of the n-butane, and the butenes-butadiene mixture wasfractionated to separate overhead irst butene-l and nailysucstantiallypure butadiene. The butene-i fraction contained some butadiene which wasrecovered by a chemical separation process utilizing a cuprous chloridereagent.

The butene-l and the butenes-Z bottoms from the final fractionation werecombined as the recycle stream to the second dehydrogenation stage,while the n-b-utane previously separated was dehydrated and returned tothe rst dehydrogenation stage. The make-up n-butane for the rst stageamounted to a. little more than 35 per cent of the total charge to thatunit since there was substantially'no loss or conversion of n-butane inthe second stage, The two-stage process as operated produced a 40 pervcent yield of butadiene based on make-up n-butane feed or a 50 per centyield based on the butenes charge to the second stage.

Example Il' butadiene. Steam was added to the charge vapors at the inletof a pre-heating furnace to produce a charge of the followingcomposition:

Volume per cent Butenes 36 Butane 25 Steam 39 This charge leitl thepreheater at 1185 F. and at the inlet to the catalyst chamber steam at1200 F. was injected, in an amount equal to about 10 volume per cent ofthe resulting total mixture. This addition offset a slight drop intemperature in the transfer line and permitted correspondingly lower`temperature in the preheater to produce an initial reaction temperatureof 1185 F. at the point of entry to. the lcatalyst case. Without steamaddition at this point, the catalyst inlet temperature was about 1180 F.

During the passage of the vapors through the catalyst, an additionalvolume of steam at 1200? F. was injected at several points in thecatalyst bed. The volume added amounted to about '7 volumeper cent ofthe resulting total vapor mixture. The exit temperature of the vaporswas 1150 F. whereas without steamviniection and at equivalent spacevelocity the 4exit temperature was 1140" F. The higher averagetemperature throughout the bed produced a higher conversion of butenesto butadiene, and the additional incremental dilution of the eilluentsincreased the recovery of the diolen without adversely affecting theequilibrium in the oleiin-diolen conversion reaction.

After processing the vapors to segregate n-butane for recycle to thefirst stage and a butenesbutadiene fraction, the latter fraction wastreated by the scheme outlined in Example l, except that both thebutene-l overhead fraction' and the butenes-2 bottoms fraction from thelast two fractionation steps were combined ahead of the chemicalextraction unit and treated for the recovery of butadiene. The butadieneyield was 55 volume per cent based on the butenes charged to the seconddehydrogenation catalyst.

While the foregoing examples have served to illustrate specificapplications of our invention, other modincations will be obvious andwithin the scope of our disclosure.

Butadiene separation may be carried out as indicated or by anysatisfactory method or combination of methods such as the use of cuprousor other metal salt reagents and/0r extraction by sulfur dioxide, or byother selective solvents.

Further, although weV usually prefer to utilize a clean-up extraction onrecycle streams to the olen dehydrogenation step, small amounts 'ofbutadiene may be'returned with said recycle streams.

The water resistant catalysts prepared and/or selected by the methodsdescribed may be reactivated over long periods of usey by treatment withoxidizing gases to, burn out carbonaceous residues responsible fordecreased activity. In this connection it has been noted that in thereactivation of our preferred water-resistant catalysts, neitherrelatively high temperatures during reactivation nor the presence ofrelatively large -amounts of water vapor in the reactivating gas rigidtemperature control during reactivation to avoid serious deterioration.

The terms water-sensitive" and water-resistant as applied to thedehydrogenation catalysts described herein are intended to indicate thedegree to which said catalysts become polsoned and/or inactive due tothe Presence of more than a trace of water vapor in the hydrocarbonsundergoing the speciiied conversions.

While the foregoing disclosure has been relatively specinc to thetreatment of C4 hydrocarbons, for the production of butadiene, we havefound that equivalent results may be obtained from the application ofour process to higher boiling paraiiins of live or six or more carbonatoms for the production of dioleiins.

We claim:

1. A pressure for the production of butadiene from normal butane whichcomprises contacting said normal butane with a dehydrogenation catalystunderl conditions effecting conversion of a portion of said normalbutane to normal butenes, and passing the C4 hydrocarbon content of theresulting ellluent, without separation into its components, in admixturewith steam into contact with a. catalyst consisting of bauxite renderedwater resistant by incorporation of a minor proportion of a compoundselected from the group consisting of the oxides and hydroxides ofbarium and strontium, under conditions effecting conversion of normalbutenes to butadiene as the principal reactionwithout substantialconversion of normal butane.

2. A process for the production of butadiene from normal butane whichcomprises contacting said normal butane with a dehydrogenation catalystunder conditions effecting conversion of a portion of said normal butaneto normal butenes, and passing the C4 hydrocarbon content of theresulting effluent, without separation into its com.. ponents, in'admixture with steam into contact with a catalyst consisting of bauxiterendered water resistant by incorporation of a minor proportion ofbarium hydroxide, under conditions effecting conversion of normalbutenes to butadiene as the principal reaction without substantialconversion of normal, butane.

3. A process for the production of butadiene from normal butane whichcomprises contacting said normal butane with a dehydrogenation catalystunder conditions eiecting conversion of a portion of said normal butaneto normal butenes, and passing the C4 hydrocarbon content of theresulting eilluent, without separation into its components, in admixturewith steam in amount sufcient to reduce the partial pressure of thebutenes in the mixture to from 0.2 to 0.5 atmosphere into contact with acatalyst consisting of bauxite rendered water resistant by incorporationof a. minor proportion of a. compound selected from the group consistingof the oxides and hydroxides of barium and strontium, under conditionseffecting conversion of normal butenes to butadiene as the principalreaction without substantial conversion of normal butane.

WALTER A. SCHULZE. J'OHN C. HILLYER. HARRY E. BRENNAN.

yCERTIFICATE oF CORRECTION. Patent No.'2,567,622 January 16, 19L5.

WALTER A. sCHUIzE, ET AL.

It is hereby certified 'that error appears `in the printed SPeCfiCatOn"`of"r:]:1eabove numbered patent requiring correction as follows: Page 1,second column, line 7, for .05 atmosphere read O.5.atmosphere; A line2li, for "acting" read "active-F.; and that the said Letters Patentshould be read with this correction therein that the same may conform tothe record of the Case in the Patenteoffice.

Signed and sealed this 21|.th day of April, A. D. 1915.

Leslie Frazer (Seal) Acting Commissioner of Patent-s.

